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The owner of a 1998 Jeep Wrangler had several questions about the use of a CompCams 252H grind camshaft in a Jeep 4.6L stroker inline six engine build. His engine core is a 1998 Jeep TJ Wrangler 4.0L...Here is our exchange. My comments are in red:
Keith M.: I’ve seen some posts, including on Comp Cams’ site, that say the head on the ’98 has different size valve stems than other years and that cams that will work on other years won’t work on this one. I’m pretty confused by what seems to be conflicting and unreliable information.
Moses: I’m not clear why there is so much confusion. CompCams should know parts interchangeability and sizing. 4.0L valve stems are available in both standard size and oversize for a given engine, which may account for the confusion. Parts interchangeability spans many years. Exhaust or intake valve head diameters may change while stem diameters remain common. Federal-Mogul is a well-known reman engine industry parts supplier. We’ll use F-M as a reference source:
https://www.fme-cat.com/overlays/part-detail.aspx?brand=SP&PartNumber=V-2527&pt=Intake%20Valve&lu=1998%20JEEP%20WRANGLER&vin= [Intake valves]
https://www.fme-cat.com/overlays/part-detail.aspx?brand=SP&PartNumber=V-4554&pt=Exhaust%20Valve&lu=1998%20JEEP%20WRANGLER&vin= [Exhaust valves]
https://www.fme-cat.com/Application.aspx?year=1998&make=JEEP&model=WRANGLER&cat=Engine&engbase=4.0L%20L6%20242cid&ga=Y&back=true [Overview of intake and exhaust valves]
https://www.fme-cat.com/overlays/part-detail.aspx?brand=SP&PartNumber=VK-216&pt=Valve%20Spring%20Retainer%20Keeper&lu=1998%20JEEP%20WRANGLER&vin= [Valve retainer keepers]
https://www.fme-cat.com/overlays/part-detail.aspx?brand=SP&PartNumber=HT-2011&pt=Valve%20Lifter&lu=1998%20JEEP%20WRANGLER&vin= [Lifters are the same over all inline Jeep/AMC sixes]
A concern with camshaft installations would be the rocker arm ratio. See the rocker arm interchangeability in this listing. AMC/Jeep inline six rocker arms are essentially the same with the same ratio:
https://www.fme-cat.com/overlays/part-detail.aspx?brand=SP&PartNumber=R-905A&pt=Rocker%20Arm&lu=1998%20JEEP%20WRANGLER&vin=
Pushrods for 4.0L engines fit the full range of 4.0L years. They are available in different lengths because the rocker arms are non-adjustable. I have discussed this at length in the forums and magazine; see https://forums.4wdmechanix.com/topic/1155-42l-re-build-77-cj-7-project/ and my reply comments from December 25, 2018 and forward. Read the details on fitting the right length pushrods. Here is the F-M parts listing for 4.0L pushrods in a standard (OEM baseline) length. There is selective fit application coverage to compensate for engine block and cylinder head deck height changes, head gasket thickness and so forth:
https://www.fme-cat.com/overlays/part-detail.aspx?brand=SP&PartNumber=RP-3275&pt=Push%20Rod&lu=1998%20JEEP%20WRANGLER&vin=
Keith M.: I want to use the 252 cam you recommend in your video but I haven’t been able to find a video with specific part numbers. Some of the information I’ve seen indicates that I need to change the valve springs if I go to that cam, other places I don’t see that. I need a timing set but have new lifters so I’m trying to get a package if I can but don’t want un-needed parts. I’m also unsure of which cam works with fuel injection as I have been told this makes a difference.
Moses: Sounds like you just need the 252H camshaft if your new lifter set is compatible. If the lifters are OEM replacement, ask CompCams tech if OEM lifters will work with the 252H camshaft. Typically, the camshaft kit includes the cam and lifters, but if CompCam simply uses an OEM replacement type lifter, you could save some here. The 1998 4.0L upper valve train (valves, retainers, keepers, rocker arms and such) should be readily compatible with your 252H camshaft choice. You do need to use the correct length pushrods to attain the right lifter preload as described at the forum exchange and magazine articles. If lifters are the same, you can see whether CompCams is willing to sell the camshaft by itself. They may not warrant the camshaft if you don’t use their lifters…Always use engine break-in lube additive (Lucas, CompCams, etc.) with ZDDP to assure proper seating of the lifters with the camshaft lobes. You still need a timing set from whatever source plus correct length pushrods if the OEM pushrods are not the correct length.
As for the PCM compatibility, there is the issue of Coil-On-Plug engines requiring a different camshaft than the 252H. Your engine is not C-O-P, it has a distributor and earlier PCM programming. I’ve not heard of anyone getting an engine code from a 252H camshaft installed in a pre-C-O-P engine like yours. If I were to build my 4.0L 1999 XJ Cherokee distributor type engine into a stroker, I would use the 252H grind camshaft rather than use a stock OEM replacement. I have used the 252H grind with EFI truck engines as far back as a Ford 300 inline six MPI engine (1987). The 252H grind has also been tested repeatedly by Tony Hewes on pre-C-O-P EFI/MPI 4.6L stroker builds.
Keith M.: This package would be fine, under specifications it says it works on years 1964-1998. But I can’t be sure that’s correct really, because of the fuel injection and possible valve stem issue:
https://www.compcams.com/high-energy-206-206-hydraulic-flat-cam-sk-kit-for-amc-199-258-4-0l.html
If I had to replace valve springs I’d use this kit:
https://www.compcams.com/high-energy-206-206-hydraulic-flat-cam-k-kit-for-amc-199-258-4-0l.html
In specifications it says 1964-1998, but under Installation Notes it states ‘K-Kits will only work in 1964-88 models due to different valve stem diameters”
Moses: Valve springs and retainer sizes are governed by the valve stem diameter. This appears to be the reference here. Logically, you do need to match valve springs and retainers to the valve stems and cylinder head spring seats. For your purposes, you only need to use the right diameter 4.0L valves, matching springs and retainers for your cylinder head casting and model year choice. Approach the valvetrain like you’re rebuilding a stock 4.0L engine. Choose replacement parts for the cylinder head casting and block casting involved.
Keith M.: And somewhere in here there’s a review for a kit where the reviewer states the kit won’t work specifically on the 1998 engine. That’s strange to me and seems incorrect- I have two heads, one is a 7120 of an earlier (1991-1995 I think) and then there’s the 0630 casting that came off my 1998. Both have 5/16 valve stem diameters by my measurement so I don’t believe there’s a difference. I’m assuming the whole problem with valve stem diameter is the earlier years are a different size so the later heads won’t work with the keepers and other valve spring parts that come in the kit.
Moses: My assumption, too. We’re in accord here…
Keith M.: I’m just trying to avoid getting the wrong cam and having it fitted to the bearings and then having to get another one. I don’t want to reuse the stock cam really, but I don’t know enough to say a different cam is worth it. This Jeep needs to idle and drive well on the street, I can’t have it be stumbly or rough idling as I will be selling it at some point soon. I do want to learn how to do these builds well as I restore IH Scouts- the 4.2 was an available engine that I think is much better in many ways than the IH engines and if I could find a way to build an excellent and reliable stroker with a 4.0 block and the 4.2 crank I’d do these regularly.
Moses: Understood, Keith…I’m a Scout buff, too. If fuel efficiency is an aim and vehicle weight not excessive, a 4.6L build from a 1991-99 (pre-C-O-P) 4.0L block and head could make sense as an alternative to the 304 or 345 I-H V-8. I-H was wise to outsource AMC 4.2L/258 engines, they offered a high-torque design that tolerated emission controls better than competitors.
Keith M: Thanks for your help Moses, I’ve done my best to sift through all the info out there and I just can’t come to the right conclusion without your advice...Respectfully, Keith M.
Moses: No problem…You want to build a safe and reliable engine. My recommendation for the 252H grind has always been simple: This grind offers increased lift with moderate duration. More lift without increased duration means a “bottom-end” camshaft that actually enhances the idle, tip-in response and mid-range power. This cam is much different than the 260H grind. Since the 1980s, I have recommended the CompCams 252H for fuel efficiency, quicker torque rise (more diesel-like), superior idle and rock crawling tip-in stability. This camshaft raises idle vacuum and maintains higher manifold vacuum from idle to mid-range rpm. This is simply a trailer pulling, rock crawling, high manifold vacuum camshaft for optimal power at low speeds, midrange and to a realistic 4500-5000 rpm maximum shift point. It will make power to 5,500 rpm in a pinch.
In your 1998-based pre-C-O-P PCM engine, you should experience no problems. The lift is not extreme and will not create valve spring “coil bind” with stock ratio rocker arms. (Valve springs must be new or in good condition and provide the proper spring rates at specified valve spring heights.) With a stroker crankshaft, the 252H makes even more “stump-pulling” sense. The gearing of your Jeep should target a 4500-5000 rpm maximum engine speed. Your single rail EFI/MPI, the 1998 PCM, MAP sensor and camshaft sensor will find this camshaft compatible. The 302 Ford V-8 injectors described in my articles will make sense.
C-O-P engine builders should consider the newer grind from CompCams to avoid engine check light issues. The C-O-P PCM and camshaft position sensor monitors the OEM camshaft valve opening/closing events (lobe valve timing). The CompCams 252H valve opening/closing events can trigger an engine check light on a C-O-P engine with its PCM programming.
A roller chain (Cloyes or similar) timing set is always an improvement, though the 252H camshaft will work with a stock/OEM replacement set as well. Your focus should be selecting the correct length pushrods and setting the valve timing to factory marks. This is optimal valve timing for the performance gains I have described…Make sure you install the distributor correctly, which will properly index the camshaft position sensor and ignition rotor in the process.
There is nothing exotic about the 252H grind. I have installed this camshaft as an OEM replacement. The valve/lobe timing creates an issue with the C-O-P engines because the later PCM is looking for specific valve opening and closing events in relationship to the crankshaft.
Let us know how your 4.6L build turns out and your impressions of the 252H camshaft performance...
Regards,
Moses